You need to first get your gastrointestinal issues under control. Those should not be lingering. That's where you doc can help.
If you're not satisfied with your doc's help for sleep, you can ask for a referral to a specialist in sleep. Nothing wrong with asking. Help is there.
If you're the self-help type, you'll also find much good info online. The gold standard is a CBT sleep training program, but again you need to address any underlying medical or psychiatric issues with your doc.